Disease in lawn grasses or turfgrasses develops from an interaction among a susceptible plant, an environment favorable for disease development, and a pathogenic organism (fungi and bacteria). Such organisms may also develop on decorative grasses, plants and crops; indeed, they may appear on any suitable organic substrate. Thus, treatment of a diseased substrate, especially turfgrass, usually consists in applying a treatment agent that will either kill the pathogen or keep it from growing.
However, the first step in disease management, and especially turfgrass disease management, should always consist in identifying the causative pathogenic agent. The knowledge of the causative pathogenic agent of a disease is important to select the most appropriate treatment agent (fungicides, bactericides etc.). Indeed, it is important to have identified the disease correctly, so that an appropriate fungicide or bactericide can be selected. Inadequate treatment will not cure the disease and may have a severe effect on the soil and other beneficial organisms. Using the wrong treatment is cost ineffective and may involve the risk of exacerbating the disease, as well as causing other unwanted side effects.
Classical methods for the identification of the causative pathogenic agent essentially rely on the symptoms which can be observed on the individual plant and on the turf stand, as well as on the pathogen structures, which can be found in the vicinity of the diseased turfgrass.
However, these methods may require a long time to be implemented, since they often involve the isolation and the culture of the pathogen in a laboratory. Besides, differentiating closely related pathogen species can be difficult.
Accordingly, molecular biology methods have been developed which circumvent these difficulties. One of the most popular fungal detection methods relies on the Polymerase chain reaction (PCR) amplification of the internal transcribed spacers (1, 2) and the 5.8S rRNA gene (ITS1-5.8S-ITS2) from the fungal rRNA operon (Goodwin et al. (1995) Plant Pathology 44:384-391; Ranjard et al. (2001) Applied and Environmental Microbiology 67:4479-4487).
For bacterial detection, PCR amplification and sequencing of the 16S rRNA gene is used (Nam H R, Lee H M, Lee Y. Isolation of quinupristin/dalfopristin-resistant Streptococcus agalactiae from asymptomatic Korean women. J Microbiol. 2008 February; 46(1):108-11. doi: 10.1007/s12275-007-0217-1. PubMed PMID: 18337702).
However, sequencing of the region of a specific primer pair is often necessary for the identification of a given pathogenic species, which renders this method cumbersome where the identity of pathogen is unknown and is sought for. Furthermore, sequencing of mixtures of pathogens is expensive and laborious. Species specific primers to identify certain species out of mixtures are not available for all microorganisms. Accordingly, these methods are not used in routine for determining the anti-pathogenic agent most adapted to treat a given turfgrass disease.
Japanese patent application No. 2008005760 discloses 458 probes for detecting molds that can be found in food. These 458 probes are designed for detecting molds by a hybridization-based method involving the use of a microarray.
Patent application WO 2009/147017 A1, of the same applicant, discloses nucleic acids and methods for detecting pathogenic fungi in turfgrass. This invention relates to turfgrass but focuses on AFLP and T-RFLP as methods for identification. This method has the limit that often many different fungal species, pathogenic and non-pathogenic, are present in turfgrass. Many different species in a complex sample make it difficult or even Impossible identifying numerical underrepresented species. The disease causing pathogenic species, however, is not necessarily the most abundant species.
As a consequence, current methods of choice for the detection of plant pathogens and beneficial microorganisms are time-consuming, not sensitive enough, not specific enough, and/or not broad enough to detect the spectrum of microorganisms.
It is therefore an objective of the present invention to provide specific nucleic acids that enable identification of the pathogens and beneficial microorganisms present in a sample.
It is also an objective of the present invention to provide a single Microarray-Chip containing up to 100 spots with these specific nucleic acids. These nucleic acids are specific for e.g. 90 known fungi and e.g. 10 bacteria species.
A further object of the present invention is a method that enables to test in a single sample for up to 100 different species. Since DNA sequences of very closely related species are identical, this method is also able to include detection of those microorganisms. This method thus makes it possible to screen very fast for many microorganisms. Furthermore, the method is adaptable for high-throughput. The method according to the invention is thus very sensitive and enables detection of pathogens that are present at low levels.